David Cameron's capture of the Conservative party leadership last year was so assured, and his subsequent repositioning of his party so audacious, that high expectations of his keynote speech at Bournemouth yesterday were inevitable. Before Mr Cameron entered the hall, delegates were shown a video that raised those expectations higher still. It highlighted a list of priorities that would have been astonishing to past Conservative conferences: public services, social justice, wellbeing, environment, global poverty, diversity and security. The "new direction" in which Mr Cameron has taken his party, and which has been the explicit theme of this week's conference, could not have been showcased more clearly.

At first Mr Cameron's speech was seamlessly of a piece. In Bournemouth, he claimed, the Tories have shown that they are back in the centre ground of British politics. The party was open to new ideas and fresh thinking. The "people's priorities" were now "our priorities" too - first among them the national health service, to which Mr Cameron pledged himself as unequivocally as any Tory leader has ever done. And there would be no return to the old policies on tax, he insisted: "They're not coming back. We're not going back."

No one who has watched the Tories this week can doubt that Mr Cameron is serious about these claims. And yet his speech, like his party's current opinion poll rating, really ought to have been better than it was. Given the strong position into which Mr Cameron's audacity has led his party, this was surely the occasion to press forward with renewed audacity, confronting the Tories with bigger decisions and tougher dilemmas than he appeared willing to do. True, the speech contained some tough stances - on abolishing the Human Rights Act, and on faith schools. But calling for Islamic schools to accept a minority of non-believers was never going to be controversial with this audience. A braver Tory leader would have echoed William Hague's words the previous day about the necessity for a Conservative government to re-engage in the European Union - but as too often there was a silence from Mr Cameron where Europe ought to be.

Mr Cameron was keen to rebut the charge that he is more style than substance, but at key moments he seemed to flunk that challenge. On Afghanistan, for example, he seemed to build up to some significant criticisms of government policy on this indisputably grave crisis. But his conclusion, that Liam Fox would be a great defence secretary, hardly matched the gravity of the issues. The environment has been at the heart of much of the new Tory leader's campaigning. And yet, although Mr Cameron threatened to tell his audience uncomfortable truths about the price they must pay for tackling climate change, he never got close to making them gasp or wince with the toughness of his prescriptions. To climax that section of his speech with a call on Mr Blair to "do something for the environment" was not just an anti-climax but a cop-out.

The big question that has faced the Conservative party this week is why it is not doing much better in the opinion polls or at the ballot box? Mr Cameron's speech was an opportunity to confront the public's doubts and the party's uncertainties. What would a Cameron government really be like? Can the Tories be trusted with the public services? Has the party of Margaret Thatcher and John Major really changed? Mr Cameron clearly understands that these are central questions. Yet his answers yesterday were hesitant. He covered his bets. He schmoozed the party as often as he challenged it. Mr Cameron was unquestionably the political star of the last 12 months. Yesterday he was frankly disappointing - and for the first time he is raising doubts about whether he has either the stomach or the strategy to lead the Tories back to power.